Steel has been manufactured quite extensively in a vessel known as the basic oxygen furnace. In this furnace, pure oxygen is blown from above into the molten iron by a lance. This process is very economical for manufacturing certain types of steels but it has a number of disadvantages in comparison with a converter that has oxygen blown from below. It requires expensive lances that are subject to a great deal of wear from splashing iron and slag and from high temperatures in the area of the stream of oxygen contacting the surface of the bath. In addition, the mixing of the bath and the equalization of concentrations, with the oxygen blowing process, is not as intensive as with a bottom blown converter. Another disadvantage is that a good deal of the oxygen passes to the melt through the slag, the iron oxide content of which is correspondingly high.
In the basic oxygen furnace process, only some of the oxygen emitted by the lance is utilized. Some of the oxygen reacts with the waste gas of the refining reactions. These gases are hard to collect and must be subjected to costly cleaning treatment. Also, heat losses arise from vaporization of the iron in the region of the burning spot, which also causes brown smoke.
The use of oxygen in bottom blown converters for making steel is not new. Sir Henry Bessemer is recognized for suggesting its use in 1856, although it was not really practical before large scale oxygen plants were developed which was about 1928. The unusually rapid wear in the converter bottom in part, from the blowing in of pure oxygen, prevented this proposal from being very successful. One reason for this rapid wear was that the bottoms were made from monolithic material by casting mixtures of refractories and baking them to high temperatures in special ovens. These bottoms were the natural outgrowth of the converted Bessemer shops.
Bottom life in bottom blown converters has been improved by utilizing refractory brick shapes. The longtime performance of brick bottoms is better than that of monolithic bottoms because of the wide ranges of properties possible in brick production compared with the narrower range of properties possible in large monolithic bottoms. Brick can be formed under pressure, fired and impregnated if desired. Further, the in-plant facility having proper fume control that would be required to heat, mix, vibrate and bake monolithic bottoms, would not be needed when brick are used. Repair of the bottoms of these vessels is made easy by utilizing a flat removable bottom or plug, which is smaller than the furnace inner diameter and separated from the stationary bottom by a monolithic refractory joint to facilitate bottom removal. The removable bottom contains multiple spaced apertures for injecting the oxygen.